Purpose :
To investigate the effect of different scanning geometries of the human cornea on intensity and polarization sensitive optical coherence tomography (OCT) data.

Methods :
A polarization sensitive swept source OCT system operating at 1060nm central wavelength was used for imaging. The instrument is based on single mode fiber optics and provides an A-scan rate of 100kHz. 3D volumes consisting of 150B-scans (1024A-scans per B-scan) are recorded in less than 2 seconds. Two different scanning geometries for imaging the human cornea in vivo are investigated. Using parallel imaging beams and a new scanning approach that uses imaging beams that are nearly orthogonal to the corneal surface. This is introduced through the implementation of an aspheric condenser lens. The instrument provides information on intensity retardation, birefringent axis orientation and degree of polarization uniformity. Changes of these parameters can be associated with the microstructure of the cornea.

Results :
Images recorded with the classical scanning pattern showed only good signal quality at the center and at the periphery (limbus) of the cornea (cf. Fig. 1A). The new scanning geometry resulted in images with high signal intensity over the entire field of view (cf. Fig. 1B). Birefringence of the cornea originates from corneal fibrils that are contained in lamellae. The cornea consists of several lamellae that are preferentially orientated parallel to the corneal surface. The fibril orientation in depth changes roughly by 90 degrees from lamella to lamella. In contrast to other incident angles low net retardation is observed for beams that are orthogonal to the surface. Thus, retardation observed with the classical scanning pattern originates from the shape of the cornea. The new scanning geometry overcomes this effect. Hence, the presence of additional corneal fibril structures could be observed.

Conclusions :
The new scanning pattern greatly enhanced the image quality of PS-OCT of the cornea. The orthogonal scan pattern reduces the influence of the corneal shape on the polarization sensitive data and allows the detection of additional fibrils that are present within the cornea.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

Fig. 1. A):B-scan intensity image of the cornea recorded with the standard scanning pattern. B) B-scan intensity image recorded with the new scanning pattern. C) Transformed image of (B) resembling the true shape of the cornea

Fig. 1. A):B-scan intensity image of the cornea recorded with the standard scanning pattern. B) B-scan intensity image recorded with the new scanning pattern. C) Transformed image of (B) resembling the true shape of the cornea